Projection television (PTV) systems in “nearly-flat” rear PTVs utilize folded-optical systems implemented by multiple-optical-path technologies (e.g. CRTS) or by single-optical-path technologies (e.g. DLP, LCD, or LCOS). The shallowness of the display's enclosure requires that the folded optical systems must be adjusted to maintain alignment of the images over the visible surface of the screen. Without proper adjustment, the images displayed on the screen by the folded-optical systems can appear shifted or rotated out of proper alignment, or exhibit a pin-cushion effect. To avoid misalignments or the pin-cushion effect, adjustments to alignment are made at the factory, but with age, temperature and other environmental conditions, or even with jostling of the unit during storage and shipping, it is often necessary to readjust the geometric alignment in the field in order to maintain the quality of the image on the screen over time or even out of the box.
Various types of alignment and convergence systems, both manual and automated, have been developed to handle the necessary adjustments. Manual systems tend to be labor intensive, tedious and extremely time consuming, requiring hours to complete. Because the manipulator must often have technical knowledge or training sufficient to execute the manual alignment and convergence corrections, abilities that ordinary PTV purchasers seldom possess, manual correction is typically accomplished by a skilled technician. In addition, because the manual procedure often requires the use of special test instruments, it may require the inconvenience of removing the PTV from the purchaser's home so that the adjustment can be made at a repair facility.
Although automated alignment and convergence systems tend to avoid the disadvantages associated with manual systems, they too have their limitations with respect to accuracy, speed, reliability and expense. One example of an automated system includes the use of a mechanically scanning optical head that samples certain predetermined areas of a projected test pattern. The various mechanical elements and motors of such a system tend to add to its cost and complexity while detracting from system reliability. In addition, convergence and alignment accuracy tends to be dependent on motor accuracy and the process still tends to require several minutes to complete.
Accordingly, it would be desirable to provide an inexpensive automated geometric alignment system that reliably achieves geometric alignment over the entire screen without increasing the complexity and cost of the system.